JPH03276752A - Semiconductor capacitance device - Google Patents

Abstract

PURPOSE:To obtain a semiconductor capacitance device having a reduction in a leakage current, sufficient insulating breakdown reliability, and excellent electric characteristics irrespective of the polarity of an applied voltage by setting the thicknesses of first and second oxide films to a specific range or less. CONSTITUTION:In a 3-layer laminated structure of a silicon oxide film 5, a silicon nitride film 6 and a silicon oxide film 7, a leakage current is determined by the film 6, and holes greatly contribute to its conducting mechanism. On the other hand, insulating breakdown reliability or life of a composite insulating film is decided according to the films 6 and 5, 7. lf the thickness of the silicon oxide film is 2.0nm or less, holes are tunneled through the silicon oxide film. Therefore, the thicknesses of the films 5, 7 are set to 2.0nm or more, and the thickness of the silicon oxide film is set to 4.0nm or more. Then, the holes can be blocked, and if the thickness of the silicon oxide film is 3.0nm or less, tunneled electrons are blocked. Then, the thicknesses are set to a range of 2.0-3.0nm, thereby reducing the leakage current.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a semiconductor capacitor device comprising a three-layer insulating film in which an oxide film, a nitride film, and an oxide film are sequentially laminated from the bottom layer on a semiconductor substrate.

[Conventional technology]

In recent years, DRAM (dynamic random access)
With the increasing integration and capacity of memory devices, memory cells have come to occupy about half of the chip size. Therefore, this memory cell is required to be miniaturized, and in order to ensure reliability as a memory,
Sufficient cell volume I (/l O femtofarano l”C
f F ) or higher) is also required. In order to satisfy these demands, in the structure of the capacitor portion of a memory cell, a trench-horizontal structure capacitor, a laminated structure capacitor, etc. having a three-dimensional structure have been proposed in place of the conventional flat plate capacitor.

A capacitor section of a conventional memory cell having a three-dimensional stacked structure will be explained based on FIG. 4.

FIG. 4 is a sectional view showing a conventional semiconductor capacitor device.

As shown in FIG. 4, an insulating film 3 is formed on a silicon substrate 1 on which a diffusion layer 2 of the same or different conductivity type as the silicon substrate 1 is formed, and a contact hole is formed in this insulating film 3. An opening X is formed.

Further, a polycrystalline silicon film 4 is formed over the opening X, and this polycrystalline silicon film 4 and the diffusion layer 2 are electrically connected.

A lower electrode is formed by processing polycrystalline silicon film 4 into a predetermined shape using photolithography and tri-etching techniques.

Next, a silicon oxide film 5' (eg, 2.5 nm thick) is formed on the polycrystalline silicon film 4, which will become the lower electrode.

A silicon nitride film 6 (for example, 11 nm thick) is formed on the silicon oxide film 5', and the surface of the silicon nitride film 6 is thermally oxidized to form a very thin silicon oxide film 7'' (for example, 11 nm thick). A film thickness of 1 nm) is formed.

Finally, a polycrystalline silicon film 8, which will become an upper electrode, is formed on this silicon oxide film 7'.

In this way, the three-dimensional stacked structure is a three-layer insulating film (hereinafter referred to as
"Composite insulation film". ) was formed.

In a semiconductor capacitive device having such a structure, the insulating film constituting the capacitive part is a composite insulating film, and the capacitive part is also formed on the side wall portion of the polycrystalline silicon film 4, which becomes the lower electrode, so that the silicon oxide film Because it has a higher dielectric constant than a flat capacitor whose capacitor part is made of an insulating film,
A large capacity can be secured with the same area occupied by the capacitor as a flat plate capacitor.

Furthermore, a polycrystalline silicon film 4 that will become a lower electrode is formed on an insulating film (not shown) with a large surface unevenness, and a polycrystalline silicon film 5'' that will become a lower electrode and a polycrystalline silicon film that will become an upper electrode. A larger capacity can be ensured by alternately arranging the electrodes 7'' in a comb shape to form a multilayer laminated structure.

[Problem to be solved by the invention] However, in such a conventional semiconductor capacitor device,
Due to its structure, the thickness of the upper and lower silicon oxide films 5'' and 7' that sandwich the silicon nitride film 6 is different from each other. In this way, the upper and lower silicon oxide films 5 that sandwich the silicon nitride film 6 If the film thicknesses of the silicon oxide films 7 and 7 are different, there may be problems such as leakage current or reduced dielectric breakdown reliability depending on the polarity of the voltage applied to the silicon oxide film 7, which is the upper electrode. Ta.

In other words, when a thin silicon oxide film 7° is formed on one of the silicon oxide films constituting the composite insulating film as in the conventional example described above, when a positive voltage is applied to this thin silicon oxide film 7'', A leakage current is generated by injecting holes into the silicon oxide films 5'', 7'' and the silicon nitride film 6.

Further, in such a composite insulating film, the dielectric breakdown reliability has little dependence on applied voltage, and a sufficient life span cannot be ensured at the operating voltage.

On the other hand, increasing the thickness of the silicon oxide film can reduce leakage current, but since the dielectric constant of the composite insulating film is dominated by the thick silicon oxide film, the capacitance also increases. be controlled. In such a case, the dielectric constant (ε-3,9) of the silicon oxide film is only 55% of the dielectric constant (ε-7) of the silicon nitride film, making it impossible to secure sufficient capacity. Further, when the silicon oxide film is thick, the dielectric breakdown reliability of the composite insulating film is also determined by the silicon oxide film. In this case, silicon oxide films generally have lower dielectric breakdown reliability than silicon nitride films, so
The dielectric breakdown reliability of the composite insulating film also deteriorates.

If the thicknesses of the silicon oxide films 5'' and 7'' formed above and below the silicon nitride film 6 are different or not appropriate, even for an applied voltage of one polarity, Even if a semiconductor capacitor device has excellent performance, since voltages of both positive and negative polarities are usually applied to the semiconductor capacitor device, the performance is influenced by the polarity of the applied voltage.

As a result, there was a problem in that the semiconductor capacitor device had extremely unbalanced performance.

In view of the above problems, it is an object of the present invention to provide a semiconductor capacitor device that can reduce the occurrence of leakage current, has sufficient dielectric breakdown reliability, and has good electrical characteristics regardless of the polarity of the applied voltage. It provides:

[Means to solve the problem]

The semiconductor capacitor device according to claim (1) includes a semiconductor substrate;
A diffusion layer formed on the surface of this semiconductor substrate, an insulating film formed on the semiconductor substrate, a contact hole formed in this insulating film, a first conductive film formed in a region including at least this contact hole, and A first oxide film formed on a first conductive film and an insulating film, a nitride film formed on this first oxide film, and a second oxide film formed on this nitride film.
oxide film and a second conductive film formed on the second oxide film, the first oxide film and the second oxide film have a thickness of 2.0 nm or more to 3.0 nm or more. The semiconductor capacitor device according to claim (2) is characterized in that, in the semiconductor capacitor device according to claim (1), the film thickness of the first oxide film and the second oxide film is in a range of On m or less. are made equal.

The semiconductor capacitor device according to claim (3) is the semiconductor capacitor device according to claim (1) or claim (2),
A nitride film is formed by nitriding the surface of the first oxide film.

The semiconductor capacitor device according to claim (4) is the semiconductor capacitor device according to claim (1), claim (2), or claim (3), wherein the surface of the nitride film is oxidized to perform second oxidation. It is formed by forming a film.

[Effect]

According to the configuration of the present invention, the film thickness of the first oxide film and the second oxide film sandwiching the nitride film is 2.5 nm or more to 3.0 nm or more.
By setting the applied voltage to be in the range of nm or less, the leakage current can be reduced by blocking the injection of holes without blocking the injection of electrons, and the impact of the applied voltage on dielectric breakdown reliability can be reduced. By increasing the dependence, it is possible to obtain a semiconductor capacitor device with improved lifetime at the operating voltage. Furthermore, by making the first oxide film and the second oxide film equal in thickness, the electrical characteristics of the semiconductor capacitive device can be improved regardless of the polarity of the applied voltage.

〔Example〕

An embodiment of the present invention will be described based on FIGS. 1 to 3.

FIG. 1 is a sectional view showing a semiconductor capacitor device according to an embodiment of the present invention.

As shown in FIG. 1, a diffusion layer 2 is formed on the surface of a silicon substrate 1.
An insulating film 3 having an opening X serving as a contact hole is formed on the silicon substrate 1.
A polycrystalline silicon film 4 (first conductive film) electrically connected to the diffusion layer 2 is formed in a region including at least Film thickness of 2.5 nm or more to become an oxide film - 3. A silicon oxide film 5 with a thickness of 2.5 nm or less is formed on the silicon oxide film 5, and a silicon nitride film 6 is formed on the silicon nitride film 6 with a thickness of 2.5 nm or more to 3 nm. ．． O
A silicon oxide film 7 serving as a second oxide film having a thickness of nm or less was formed, and a polycrystalline silicon film 8 (second conductive film) serving as an upper electrode was formed on this silicon oxide film 7.

The details of the embodiment will be explained below.

As shown in FIG. 1, an N-type diffusion layer 2 is formed on a P-type silicon substrate 1 by selective diffusion technology.
A silicon oxide film (not shown) having a thickness of about 150 nm was deposited thereon by low pressure CVD. Openings X, which will become contact holes, were formed at predetermined locations on this silicon oxide film by photolithography and dry etching techniques. Polycrystalline silicon, which will become the first conductive film containing phosphorus (P) at a doping concentration of 3 x ] O''cm-3, is deposited on the opening X, the diffusion layer 2 and the silicon oxide film 3 by low-pressure CVD. A film 4 of about 400 nm was deposited.Then, this polycrystalline silicon film 4 was patterned into a wiring shape by photolithography and dry etching to form a lower electrode.

Next, for example, in an oxidizing atmosphere at a temperature of 750°C and into which trichloroethane (inflow rate somg/min) was introduced,
The surface of the polycrystalline silicon film 4 serving as the lower electrode was oxidized to form a silicon oxide film 5 having a thickness of 2.5 nm and serving as the first oxide film.

Next, a silicon nitride film 6 having a thickness of 11 nm was formed on the silicon oxide film 5 by low pressure CVD.

At this time, a silicon nitride film (not shown) may be formed by nitriding the surface of the silicon oxide film 5.

Next, at a temperature of 900°C, trichloroethane (inflow amount of 500
, mg/min) and oxygen (inflow rate 8ffi/min) at 90%
By flowing the water for a minute, the surface of the silicon nitride film 6 was oxidized to form a silicon oxide film 7 having the same thickness as the silicon oxide film, 2.5 nm.

Note that the silicon oxide film 7 contains 2% to 20% nitrogen.
Contains some degree.

Then, on the silicon oxide film 7, a second film containing phosphorus (P) with a doping concentration of 3×10”cm−3 is formed by low pressure CVD.
A polycrystalline silicon film 8, which will become a conductive film, is deposited to a thickness of about 200 nm, and this polycrystalline silicon film 8 is patterned by photolithography and dry etching techniques to form an upper electrode constituting the capacitor section Y.

In this example, polycrystalline silicon films 4 and 7 were used as the upper and lower electrodes, but at least one of the upper and lower electrodes was made of metal such as tungsten and molybdenum or titanium nitride. It is also possible to use a conductive substance.

A major feature of the semiconductor capacitor device of this embodiment is that the thickness of the silicon oxide film 5 serving as the first oxide film and the silicon oxide film 7 serving as the second oxide film is 2.5 nm or more to 3.5 nm or more. On
m or less.

Silicon oxide film 5. Three-layer stacked structure of silicon nitride film 6 and silicon oxide film 7 (hereinafter referred to as "composite insulating film")
, the leakage current is determined by the silicon nitride film 6, and its conduction mechanism is Pool-Fre
This is nkel type conduction, and holes greatly contribute to this conduction.

Therefore, in order to reduce leakage current, a silicon oxide film is required to have a thickness that acts as a barrier to holes, which are largely involved in conduction. According to our study, the thickness of the silicon oxide film that acts as a barrier to holes is 2.0
It became more than nm.

On the other hand, the dielectric breakdown reliability or lifetime of the composite insulating film is determined by the silicon nitride film 6 and the silicon oxide film 57.

For example, when the thickness of the silicon oxide film is 2.0 nm or less, holes tunnel through the silicon oxide film, so the lifetime is
Determined by the silicon nitride film. At this time, the dielectric breakdown reliability of the composite insulating film is not very dependent on the applied voltage, so even if a high voltage is applied, the lifespan will not be significantly degraded. However, it doesn't last very long.

From the above, the thickness of the silicon oxide film 5.7 is set to 2.0 nm.
It was determined that it was more than m.

In addition, 4. silicon oxide film. When the thickness of the silicon oxide film is On m or more, holes can be blocked by the silicon oxide film of this thickness, but at the same time, when the thickness of the silicon oxide film is less than 3.0 nm, holes are tunneled. Electrons are also blocked.

Therefore, in this case, the dielectric breakdown reliability of the composite insulating film is
It is determined by the upper and lower silicon oxide films, and the lifetime is also determined by the upper and lower silicon oxide films.

However, since a silicon oxide film generally has lower dielectric breakdown reliability than a silicon nitride film, the dielectric breakdown reliability of the composite insulating film deteriorates.

Furthermore, when such a thick silicon oxide film is formed, the dielectric constant of the composite insulating film is dominated by the silicon oxide film, and the dielectric constant of the silicon oxide film (ε-3,
9) has only 55% of the dielectric constant (ε-7) of the silicon nitride film, so the capacitance of the composite insulating film decreases.

Therefore, from the above, the thickness of the upper and lower silicon oxide films 5 and 7 sandwiching the silicon nitride film 6 is set to be 2.0 m or more to 3 m.
It is necessary to select a range of 0 nm or less.

In this way, the silicon oxide film 5 which becomes the first oxide film and the second
The film thickness of the silicon oxide film 7 which becomes the oxide film of 2. On
m or more~3. By setting it in the range of On m or less, the leakage current can be reduced and the reliability of dielectric breakdown can be improved, and furthermore, by making the thickness of the upper and lower silicon oxide films 5 and 7 the same, the voltage can be applied. A semiconductor capacitor device having good electrical characteristics regardless of voltage polarity can be obtained.

The semiconductor capacitor device of this embodiment (the film thickness composition ratio of silicon oxide film 5/silicon nitride film 6/silicon oxide film 7 is 2.5
5 nm/11 nm/2.5 nm) and 5 conventional semiconductor capacitor devices (film thickness composition ratio of silicon oxide film 7″/silicon nitride film 6/silicon oxide film 5″)
FIG. 2 shows the measurement results of the voltage-current characteristics when a positive voltage was applied to the upper electrode (polycrystalline silicon film 8) of the layer (m/11 nm/2.5 layer m).

In FIG. 2, the horizontal axis shows the applied voltage [■], the vertical axis shows the leakage current (A), and a shows the semiconductor capacitor device of the embodiment, and b shows the semiconductor capacitor device of the conventional example.

As is clear from FIG. 2, the semiconductor capacitor device a of the embodiment has a silicon oxide film 5.7" thick (2.5 m) thick, and has a silicon oxide film 7" thin (1 nm) thick. It can be seen that the leakage current is reduced compared to the conventional semiconductor capacitor device.

In other words, in the semiconductor capacitor bag zb of the conventional example, the silicon oxide film 7'' is thin, so holes that contribute significantly to conduction are injected, whereas the silicon oxide film 7'' of the semiconductor capacitor device a of the embodiment This is because the film 5.7 has a thickness that blocks holes.

Although FIG. 2 shows the case where a positive voltage is applied to the polycrystalline silicon film 68 serving as the upper electrode, even when a negative voltage is applied to the upper electrode, the semiconductor capacitor device a of the embodiment
Since the silicon oxide film 5 and the silicon oxide film 7 sandwiching the silicon nitride film 6 have the same thickness and are symmetrical, characteristics almost the same as those shown in FIG. 2 are exhibited.

Furthermore, the temperature under measurement conditions was 900°C.

Next, FIG. 3 shows the results of applying a positive voltage to the upper electrode (polycrystalline silicon film 8) of the semiconductor capacitor device a of the embodiment and the semiconductor capacitor device A of the conventional example and measuring the time until destruction.

In Figure 3, the vertical axis shows the time (S) until the cumulative failure reaches 50%, the horizontal axis shows the applied voltage [■], and a
1 shows a semiconductor capacitor device of the embodiment, and b shows a conventional semiconductor capacitor device.

As is clear from FIG. 3, the semiconductor capacitor device a of the embodiment
Compared to conventional semiconductor capacitor devices, the applied voltage has a higher dependence on the cumulative failure time, and especially in the low voltage region, which is the actual operating voltage, the reliability of dielectric breakdown is much lower than that of conventional semiconductor devices. It can be seen that it has excellent properties and has a long life.

In other words, the life of a conventional semiconductor capacitor device having a thin silicon oxide film 7 is determined by the silicon nitride film 6, and although the life does not deteriorate much in the high voltage region, it does not depend much on the applied voltage, so On the other hand, the life of the semiconductor capacitive device a of the embodiment is largely dependent on the applied voltage, and the life is not increased even in the low voltage region where the actual operating voltage is. can be made longer.

Note that the semiconductor capacitor devices of the embodiment and the conventional example that were the objects of measurement were the same as those used to measure the above-mentioned voltage-current characteristics (FIG. 2).

Furthermore, the temperature under measurement conditions was 900'C.

Note that this embodiment simply uses a silicon substrate 1 without a pattern.
Although a capacitor section made of a composite insulating film having polycrystalline silicon films 4 and 8 as electrodes is formed thereon, other elements such as transistors may be provided on the silicon substrate forming the capacitor section. Further, the capacitance may be increased by forming the polycrystalline silicon film constituting the capacitor portion into a multilayer structure, for example, a comb-shaped structure, instead of two layers.

〔Effect of the invention〕

According to the semiconductor capacitor device of the present invention, the first
The film thickness of the oxide film and the second oxide film is 25 nm or more to 3.
By setting the range to less than On m, it is possible to reduce leakage current by blocking the injection of holes without blocking the injection of electrons, and to prevent dielectric breakdown (3 By increasing the dependence of the applied voltage on the buccal properties, the lifetime at the operating voltage can be improved.Furthermore, the first oxide film and the second oxide film
By adjusting the thickness of the oxide film within the above-mentioned range and with the same thickness, it is possible to obtain a semiconductor capacitor device that has good electrical characteristics regardless of the polarity of the applied voltage, resulting in even higher integration. and high performance.

[Brief explanation of the drawing]

Part 1 is a cross-sectional view showing a semiconductor capacitor device according to an embodiment of the present invention, FIG. 2 is a cross-sectional view showing the relationship between applied voltage and leakage current of the semiconductor capacitor device of the embodiment and a conventional example. and conventional semiconductor capacitance] 9 Diagram showing the relationship between the applied voltage of the device and the cumulative failure time, No. 4
The figure is a sectional view showing a conventional semiconductor capacitor device. DESCRIPTION OF SYMBOLS 1... Silicon substrate (semiconductor substrate), 2... Diffusion layer, 3... Insulating film, 4... Polycrystalline silicon film (first conductive film), 5... Silicon oxide film (first conductive film) 1 oxide film),
6... Silicon nitride film (nitride 11), 7... Silicon oxide film (second oxide film), 8... Polycrystalline silicon film (
second conductive film), X...opening (contact hole)
0 ---Siritsu Z base m (key special 4 + base) ・-ji, diffused - absolute R flight---Refined silicon film (first conductive film) ・-Wrinkled silicon film (first base) Uhi membrane) - 11 yen 4 Hishirifun hood (
Nichii l: Torso) -- One needle Ihishiritsun Ken (membrane on the second hame) --- Riyamakiri Shi1 Notsun 朦 (Second Yong Lending) - 阘n
(Contour 2 holes) Figure 339

Claims (4)

[Claims] (1) A semiconductor substrate, a diffusion layer formed on the surface of this semiconductor substrate, an insulating film formed on the semiconductor substrate, a contact hole formed in this insulating film, and a region formed at least including this contact hole. a first conductive film; a first conductive film formed on the first conductive film and on the insulating film;
a nitride film formed on this first oxide film, a second oxide film formed on this nitride film, and a second conductive film formed on this second oxide film. The film thickness of the first oxide film and the second oxide film is set to 2.
A semiconductor capacitor device characterized in that the thickness is in a range of 0 nm or more and 3.0 nm or less. (2) The semiconductor capacitor device according to claim (1), wherein the first oxide film and the second oxide film have the same thickness. (3) The semiconductor capacitor device according to claim (1) or claim (2), wherein the nitride film is formed by nitriding the surface of the first oxide film. (4) The semiconductor capacitor device according to claim (1), claim (2), or claim (3), wherein the second oxide film is formed by oxidizing the surface of the nitride film.